PARA-AMINOBENZOIC ACID USED AS A MARKER FOR COMPLETENESS OF 24-HOUR URINE - ASSESSMENT OF CONTROL LIMITS FOR A SPECIFIC HPLC METHOD

Objective and design: The study comprised three protocols. Protocol 1 compared a HPLC method with the commonly employed colorimetric diazaco upling method. Protocol 2 examined, if the last dosage of p-aminobenzo ic acid (PABA) could be advanced in the old to allow for a delayed age -dependent urinary excretion of PABA. Protocol 3 established limits fa r recovery of PLEA in 24 h urine applying the HPLC method Subjects and setting: A total of 151 healthy volunteers participated in the study of which 140 were accepted. In protocol 1:37 subjects aged 20-78 y wer e included. All subjects took PABA as recommended (80 mg orally at 08. 00, 12.00 and 18.00 h). Protocol 2: compared urinary PABA excretion in two groups of 80 y old subjects who had their last PABA dosage admini stered at 15.00 h (n = 16) and at 18.00 h (n = 31), respectively. Prot ocol 3: comprised 56 subjects aged 20-80 y. In the younger age group ( 20-59 y; n = 34) PABA was taken as recommended, whereas in the older a ge group (60-80 y; n = 22) the last PABA dosage was advanced three hou rs. Results: Protocol 1: HPLC gave significantly lower PABA recovery r esults compared to colorimetry, the difference between methods being 2 3.9 +/- 5.5 mg/24 h (P < 0.001). Protocol 2: higher PABA recoveries we re demonstrated with the advanced dosage schedule compared to the reco mmended schedule (208 +/- 14 mg/24 h vs 181 +/- 22 mg/24 h; P < 0/001) . Protocol 3: PABA recovery with HPLC was 211 +/- 12 mg/24 h, and the lower limit comprising 95% of subjects was 187 mg/24 h. Similar PABA r ecoveries were demonstrated in the younger subjects and the older subj ects (211 +/- 11 mg/24 h vs 211 +/- 13 mg/24 h; NS). Conclusion: An ad vanced dosage schedule for PABA in the aged is recommended. Because of lower recoveries with HPLC, the low limit For recovered PABA in a com plete 24 h urine differs from the limit based on colorimetry. This stu dy found a limit of 187 mg/24 h corresponding to the lower 95% confide nce limit for a single subject.